Process for preparing stable essentially water-free slurries of nitrocellulose and products thereof

ABSTRACT

A PROCESS FOR FORMING ESSENTIALLY WATER-FREE STABLE SLURRIES OF PLASTISOL NITROCELLULOSE WHEREIN PLASTISOL GRADE NITROCELLULOSE AND OTHER SOLIDS SUCH AS CYCLOTETRAMETHYLENETETRANITRAMINE, ARE MIXED WITH AN ORGANIC LIQUID DILUENT CAPABLE OF FORMING AN AZEOTROPE WITH WATER, SUCH AS HEPTANE, AND A STABILIZING AMOUNT OF METRIIOL TRINITRATE, AND WHEREIN THE AZEOTROPE IS VOLATILIZED FROM THE MIXTURE TO FORM THE RESULTANT ESSENTIALLY WATER-FREE SLURRY. IN ADDITION, ESSENTIALLY WATER-FREE STABLE SLURRIES CONTAINING PLASTISOL NITROCELLULOSE MADE BY THE ABOVE PROCESS ARE ALSO PROVIDED.

United States Patent M PROCESS FOR PREPARING STABLE ESSENTIALLYWATER-FREE SLURRIES 0F NITROCELLULOSE AND PRODUCTS THEREOF Albert T.Camp, Indian Head, Md., assignor to the United States of America asrepresented by the Secretary of the Navy No Drawing. Filed Oct. 23,1970, Ser. No. 83,659

Int. Cl. C06b /02 U.S. Cl. 149--92 8 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION This invention relates generally toessentially waterfree stable compositions of propellant and explosiveingredients and more particularly "to a process for preparingessentially water-free stable slurries containing plastisolnitrocellulose and the products thereof.

The hazards of handling and processing various propellant and explosiveingredients in a dry condition is well known. Handling materials of thisnature, such as cyclotrimethylenetrinitramine (RDX),cyclotetramethylenetetranitramine (HMX), and plastisol nitrocellulose,in a bone dry state is particularly hazardous owing to the likelihood ofan electrostatic and deflagration detonation. Thus, in most instancesthese materials are stored and handled in a liquid medium, usuallyWater.

However, the Water must be removed from the propellant ingredient, suchas plastisol nitrocellulose, before the mixing of the final propellantor explosive composition. Traditionally, for safety reasons, the wateris not removed from the plastisol nitrocellulose until immediately priorto the final stages of the mixing. Moreover, past processes to removeresidual water have been ineffective and even small quantities (0.10.2percent) of water react adversely with the other ingredients, such asenergetic fuels and oxidizers, high energy cross-linking agents andother additives normally incorporated in propellant and explosiveformulations.

Recently, a vast amount of interest has been directed to the developmentof composite modified double base, as well as strictly double basepropellants. A composite modified double base propellant is one in whichoxidizers, such as HMX and RDX, are incorporated along withnitrocellulose.

Thus, in view of the present day problems associated with storage ofpropellant ingredients of this nature in Water and the removal of thewater thereof, a need exists for a more convenient and effective way tosafely ship and store these ingredients, which will not hinder theirreactivity or compatibility in the final propellant formulations.

SUMMARY OF THE INVENTION Accordingly, one object of the presentinvention is to provide a process for preparing essentially Water-freestable compositions containing plastisol nitrocellulose.

Another object of the present invention is to provide a 3,723,267Patented Mar. 27, 1973 process for preparing essentially water-freestable compositions containing plastisol nitrocellulose and eithercyclotrimethylenetetranitramine or cyclotetramethylenetetranitramine.

Still another object of the instant invention is to provide essentiallywater-free stable compositions containing plastisol nitrocellulose whichcan be safely transported and stored and which are compatible and do notrender adverse effects upon the final propellant or explosiveformulation.

A still further object of this invention is to provide essentiallywater-free compositions containing plastisol nitrocellulose and eithercyclotrimethylenetetranitramine or cyclotetramethylenetetranitraminewhich can be safely transported and stored and which are compatible anddo not render adverse effects upon the final propellant or explosiveformulation.

Another object of the instant invention is to provide essentiallywater-free stable compositions containing plastisol nitrocellulose orcompositions containing plastisol nitrocellulose and eithercyclotrimethylenetetranitramine or cyclotetramethylenetetranitraminewhich when mixed therein improve the aging and mechanical properties ofthe final propellant composition.

These and other objects are achieved by providing a process whereinplastisol nitrocellulose, or plastisol nitrocellulose andcyclotrimethylenetrinitramine or plastisol nitrocellulose andcyclotetramethylenetetranitramine are mixed with metriol trinitrate anda diluent capable of forming an azeotropic mixture with water and uponthe evaporation of the azeotrope from the mixture a stable andessentially water-free slurry is formed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with thisinvention, it has been discovered that it is possible to form stable andessentially Water-free slurries of plastisol nitrocellulose by theadmixture of plastisol nitrocellulose and the other solids, if desired,i.e., cyclotrimethylenetrinitramine or cyclotetramethylenetetranitramineand a suitable diluent, which is capable of forming an azeotrope withwater, in a conventional propellant mixer. After the addition of thediluent to the solids in the mixer, metriol trinitrate is then added andthe complete mixture is thoroughly agitated under vacuum untilhomogeneity and the complete removal of the azeotrope are achieved.

Although the manner in which the ingredients are added to the mixer andagitated is not critical, the preferred manner is dependent upon severalconsiderations. For example, if the plastisol nitrocellulose and othersolids contain a large quantity of water, it is advantageous to add thediluent to the plastisol nitrocellulose and solids and agitate prior tothe addition of the metriol trinitrate. If, in turn, large quantities ofplastisol nitrocellulose and the other solids are employed and onlysmall quantities of the diluent, then to avoid lumping andnon-homogeneity it is preferable to add the metriol trinitrate to theother ingredients before agitation commences. However, in summary, thediluent, plastisol nitrocellulose and other solids should be added andmixed together before the addition thereto of the metriol trinitrate forthe most efiicient removal of water.

Plastisol nitrocellulose is a highly densified form of ballnitrocellulose. However, any nitrogen content plastisol nitrocelluloseis applicable for the purposes of this invention.

As hereinbefore discussed, all the mixing is performed under vacuumconditions and sufficient heat is supplied to enable the volatilizationof the azeotrope from the mixture. If the plastisol nitrocellulose andother solids are mixed with the diluent prior to the addition of themetriol trinitrate, it is essential that the metriol trinitrate be addedbefore all the diluent has evaporated. As the azeotrope is removed, themilky white slurry texture of the mixture becomes thicker until all theazeotrope has been volatilized at which time the slurry is essentiallywater-free and has a toothpaste constituency. It is then removed fromthe mixer.

Diluents which are within the scope of the present invention are organicliquids which are immiscible with water and are also capable of formingan azeotrope with water. Specifically some diluents encompassed hereininclude, for example, heptane, hexane, toluene, benzene and the like.

The amount of diluent employed within the process of this invention isdependent upon the quantity of water present in the plastisolnitrocellulose and other solids which has normally been quantitativelypre-determined. Thus a sufiicient amount of diluent necessary to removeall the water is utilized.

As the azeotrope vapor is removed from the remaining mixture, this vaporis condensed and the water and diluent, being immiscible, are inseparate layers and thus are easily separated from one another.

A copending application, Navy Case No. 50,615, by L. Henderson and C.Johnson entitled Azeotropic Removal of Water From Ordnance discloses theconcept of forming an azeotrope to remove residual water frompropellants and the disclosure is incorporated herein.

The quantities of materials employed in the process of the presentinvention may vary over a wide range. Actually, any proportion of theplastisol nitrocellulose and other solids may be used perhaps dependingupon specific characteristics desired in a final propellant formulation.However, in some instances, the solids may settle out of the slurry.Stable slurries are formed, however, when plastisol nitrocellulose inamounts of from about 50 percent by weight,cyclotrimethylenetrinitramine or cyclotetramethylenetetranitramine inamounts of from about to 70 percent by weight and metriol trinitrate inamounts of from about 30 to about 95 percent by weight are employed.

Accordingly, the resultant stabilized plastisol nitrocellulose andmetriol trinitrate slurry or plastisol nitrocellullose,cyclotrimethylenetrinitramine and metriol trinitrate slurry or theplastisol nitrocellulose, cyclotetramethylenetetranitramine and metrioltrinitrate slurry formed by the process of this invention areessentially water-free (0.01 percent) and are useful as mainintermediates for plastisol nitrocellulose based propellants andexplosives. They can be safely and readily shipped in this state and donot harden or cure under normal storage conditions until otheringredients are added.

Obviously, to form the final propellant or explosive, other particulateingredients and active co-plasticizer, such as triethyleneglycoldinitrate and diethyleneglycol dinitrate along with other energeticplasticizers, stabilizers and conventional cross-linkers are added tothe slurry.

Having generally described the invention the following examples aregiven for purposes of illustration. It will be understood that theinvention is not limited to these examples, but is susceptible todifferent modifications that will be recognized by one of ordinary skillin the art.

EXAMPLE 1 327 grams dry basis of plastisol nitrocellulose containingfrom about 0.15 to 0.25 percent by weight water and 40 grams of heptanewere added to a 60 LP ARC propellant mixer at 120 F. under vacuum andbriefly agitated. 510 grams of metriol trinitrate was then added to thismixture with continued agitation for about minutes. After this time anadditional 163 grams dry basis of plastisol nitrocellulose was added tothe mixture and agitated for another 10 minutes at 120 F. under vacuum.The slurry which had a toothpaste constituency, was then removed fromthe mixer and stored.

EXAMPLE 2 A slurry of 110 grams of heptane and 500 grams dry basis ofClass A cyclotrimethylenetrinitramine containing from about 0.15 to 0.25percent by weight of water and alcohol was premixed and then added tograms dry basis of plastisol nitrocellulose (about 0.15 to about 0.25percent water) in a 60 LP ARC propellant mixer. 200 grams of metrioltrinitrate was then added to the mixer and the total slurry mixture wasfurther agitated under vacuum at 120 F. for 45 minutes after which timethe water-heptane azeotrope was completely evaporated. The slurry whichhad a white color and of a toothpaste constituency was removed andstored.

EXAMPLE 3 A slurry of 60 grams of heptane and 200 grams of 18 micronsize cyclotetramethylenetetranitramine containing from about 0.15 to0.25 percent by weight of water and alcohol was prepared and then addedto 50 grams dry basis of plastisol nitrocellulose (about 0.15 to about0.25 percent water) in a 60 LP ARC propellant mixer and brieflyagitated. 200 grams of metriol trinitrate was then added to the mixerand further agitated under vacuum at 120 F. for 20 minutes. At the endof this time, 50 additional grams of metriol trinitrate was added to themixture and the resultant slurry was mixed for 30 minutes under vacuumat F.

The slurry compositions of this invention did not decompose or exhibitany phase separation after storage for four months and upon analysis hada water content of only 0.01 percent.

Thus, in accordance with the process of the present invention, plastisolnitrocellulose no longer need be stored and shipped in water, but may beshipped or stored in the stable, safe, and convenient essentiallywater-free slurry form herein provided. Moreover, the normally presentresidual Water which would react adversely with energetic fuels andoxidizers is hereby essentially completely eliminated.

It has been found also that the complete removal of the water from theplastisol nitrocellulose and other solids at such an early stage in thefinal propellant formulation, reduced shrinkage and increased thecastable life of the final compositions are provided.

Obviously, numerous modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the appended claimsthe invention may be practiced otherwise than as specifically describedherein.

Having thus described the invention, what is claimed and desired to besecured by Letters Patent of the United States is:

1. A process for preparing stable, essentially waterfree slurries ofplastisol nitrocellulose consisting of:

mixing moisture wet plastisol nitrocellulose with an organic liquiddiluent immiscible with water and capable of forming an azeotrope withwater, and selected from the group consisting of heptane, hexanetoluene, and benzene, in a sufiicient amount to remove all the waterfrom the plastisol nitrocellulose, whereby an azeotropic mixture ofwater and said diluent is formed;

adding and mixing a stabilizing amount of metriol trinitrate to theresultant mixture; and

volatilizing the formed water diluent azeotrope from the resultantslurry.

2. A process for preparing stable, essentially waterfree slurries ofplastisol nitrocellulose which consists of:

mixing moisture-wet plastisol nitrocellulose and a moisture-wet solidselected from the group consisting of cyclotrimethylenetrinitramine andcyclotetramethylenetetranitramine with an organic diluent immisciblewith water and capable of forming an azeotrope with water, and selectedfrom the group consisting of heptane, hexane, toluene and benzene, in asufficient amount to remove all the water from the plastisolnitrocellulose and other solid, whereby an azeotropic mixture of waterandsaid diluent is formed;

adding and mixing a stabilizing amount of metriol trinitrate to theresultant mixture; and

volatilizing the formed water-diluent azeotrope from the resultantslurry.

3. The process of claim 1 wherein the organic liquid diluent is selectedfrom the group consisting of heptane and hexane, the plastisolnitrocellulose is mixed in amount which results in an essentiallywater-free slurry of from about to about 50 percent plastisolnitrocellulose and the remainder being metriol trinitrate.

4. The process of claim 2 wherein the organic liquid diluent is selectedfrom the group consisting of heptane and hexane, the plastisolnitrocellulose is mixed in an amount which results in an essentiallywater-free slurry of from about 5 to about 50 percent by Weightplastisol nitrocellulose, and the cyclotrimethylenetrinitramine or thecyclotetramethylenetetranitramine is mixed in an amount which results infrom about 20 to about 70 percent by weight of the slurry and remainderbeing metriol trinitrate.

5. A stable, essentially water-free slurry consisting of plastisolnitrocellulose and metriol trinitrate.

6. The slurry of claim 5 wherein the plastisol nitrocellulose is presentin an amount of from about 5 to about percent of the total mixture.

7. A stable, essentially water-free slurry consisting of plastisolnitrocellulose, metriol trinitrate and a solid selected from the groupconsisting of cyclotrimethylenetrinitramine andcyclotetramethylenetetranitramine.

8. The slurry of claim 7 wherein the plastisol nitrocellulose is presentin an amount of from about 5 to about 50 percent by weight and themetriol trinitrate is present in an amount of from about 30 to percentby weight of the total mixture.

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